1. Field of the Invention
The present invention relates generally to a semiconductor wafer polishing machine, and more particularly to a semiconductor wafer polishing machine which polishes a semiconductor wafer by controlling the polishing pressure.
2. Description of the Related Art
As semiconductor devices have recently become larger scale and consisted of multiple layers, it has become more important to accurately plane a semiconductor wafer in the process of manufacturing the semiconductor devices. To plane the semiconductor wafer, a polishing liquid is supplied to an area between the semiconductor wafer and polishing pad, and the semiconductor wafer and the polishing pad are moved relatively to each other and pressed against each other so that the semiconductor wafer can be polished.
In order to accurately polish the semiconductor wafer, pressure between the semiconductor wafer and the polishing pad (hereinafter referred to as polishing pressure) must be precisely controlled, and further, the semiconductor wafer and the polishing pad must be maintained in a parallel position.
In a conventional semiconductor wafer polishing machine, an air cylinder is used to apply the polishing pressure, and the polishing pressure is controlled by controlling the output of the air cylinder.
The air cylinder, however, has a disadvantage because it cannot precisely control its output, and the output is pulsating. For this reason, the polishing pressure cannot be precisely controlled in the above-mentioned machine.
There is another polishing machine which swings the semiconductor wafer in accordance with the inclination of the polishing pad by supporting a wafer mount plate via a spherical bearing so as to maintain the semiconductor wafer and the polishing pad in parallel to each other.
The spherical bearing, however, has a frictional resistance, and thus the wafer mount plate cannot move completely in accordance with variations in the inclination of the polishing pad in the above-mentioned machine. Further, the uniform polishing pressure cannot be applied on the whole surface of the semiconductor wafer to be polished. For this reason, the semiconductor wafer cannot be uniformly polished.